Gennadii N Grachev

Carbon nitride coatings are synthesized in the new laser plasma of powerful optical pulsating discharge using acetonitrile as a precursor. A high-pressure and -temperature C3N4 cubic phase with a spin

It is shown that the localisation radius and the spectrum of intense sound produced by an optical pulsating discharge in the air depend on the power and repetition rate of the repetitively pulsed laser radiation, which is associated with a manifestation of the wave merging mechanism and sound absorption in the air. The experiment makes use of a CO2 laser with a power of ~1.5 kW and a repetition rate of microsecond pulses of ~50 kHz.

Spectrum and localization of intense sound produced by pulsating optical discharge is studied. It was shown that the spectrum structure and localization of sound field depends on average power and pulse repetition rate of laser radiation. Intensity and structure of the sound spectrum determination depending on the distance to pulsating optical discharge is considered. Results are confirmed in experiments where the pulsating optical discharge was created using 2 kW average power CO₂-laser (pulse repetition rate f ~ 50 kHz, pulse duration ~ 1 µs).

For applications of laser-plasma cladding, a numerical simulation of the processes occurring during the falling molten droplets (20÷200 µm) onto a cold surface (20÷600 °C), followed by solidification. Drop temperature, drop rate and other parameters typical for intense heating (~10⁵ W/cm²) during laser-plasma cladding.

A new method of laser plasma deposition had been applied to synthesise the silicon carbonitride (SiCN) coatings on stainless steel substrates and cutting devices using hexamethyldisilazane Si₂NH(CH₃)₆ as a precursor. The precursor vapours were activated by powerful optical pulsating discharge in a high velocity gas stream (Ar). Characterisation of the films has been carried out by complex methods. The deposited coatings are amorphous, uniform in thickness and decorate surfaces of different engineering materials quite well. The nanohardness of SiCN coatings was estimated as 15–24 GPa.

Results of laboratory experiments on nonlinear propagation of high-power pulse-periodic and continuous CO₂ laser radiation in a gas medium are presented. The experiments were carried out in a cell filled with a mixture of air and carbon dioxide in different partial concentrations (∼1–4%) under strong absorption and thermal blooming of laser radiation. The experimental conditions simulated the atmospheric propagation of high-power laser radiation along a kilometer-long path. Sharply focused laser beams were used; the regions of heat release along the beam channel were recorded by the shadow imaging technique. We found that, despite increased intensity, the focal waist of a laser beam is characterized by reduced heat release as compared to that in the pre- and postfocal beam regions. The saturation effect of the resonance absorption coefficient of CO₂ at high pulse peak intensity (blooming effect) is considered as the most probable physical cause of the above feature. For continuous radiation, this effect is much weaker.